Side supports with adjustable center of gravity

ABSTRACT

An apparatus is used for coupling a test head to a mounting unit such as a cradle in which the test head pivots. A base is attachable to a test head. An extension member extends away from the test head. A slider slides away from and towards a center of gravity of the test head. The slider is attachable to the mounting unit. An adjustment member extends from the extension member for fixing the position of the slider relative to the base.

This application claims the benefit of provisional application No.60/234,037, filed Sep. 20, 2000.

BACKGROUND OF INVENTION

In the automatic testing of integrated circuits (IC) and otherelectronic devices, it is desirable to bring the device to the propertemperature and to place the device to be tested in position. To performthese steps, an apparatus which is referred to as a device handler maybe used. A device handler may include a wafer prober or any otherapparatus that might hold the device being tested. The electronictesting itself is provided by a large and expensive automatic testingsystem, which includes a test head, which has been required to connectto and dock with the device handler. In such testing systems, the testhead has been usually very heavy—on the order of 40 to 1000 (or more)kilograms. The reason for this heaviness is because a test head isdensely packaged with electronic circuits in order to achieve accuratehigh speed testing.

Test head positioner systems may be used to position the test head withrespect to the device handler. When the test head is accurately inposition with respect to the device handler, the test head and thedevice handler are said to be aligned. When the test head and devicehandler are aligned, the fragile test head and device handler electricalconnectors can be brought together (i.e. docked), enabling the transferof test signals between the test head and the device handler. Thus,before being brought together, the fragile test head and device handlerelectrical connectors must be precisely aligned to avoid damaging thefragile electrical connectors.

Test head positioners are designed in several configurations, eachconfiguration being desirable for a particular purpose. Many positionersinclude a test head “mounting unit.” The mounting unit supports the testhead and may provide one or more axes of motion for the test head. Thetest head mounting unit may comprise a “pivot cradle,” a “translationcradle”, a “yoke,” or other apparatus. Generally, a pivot cradle, atranslation cradle, and a yoke all comprise two parallel structures,which are arranged next to the two opposite sides of the test head andto which the test head is attached. With a pivot cradle the test head ismounted in such a way that it can pivot about an axis, which isgenerally orthogonal to the two parallel structures. With a translationcradle the test head is mounted in such a way that it can slide in andout, and possibly also pivot. With a yoke, the test head is rigidlyattached to the two parallel structures. Examples of other structuresare mentioned later. Hereinafter, the term “cradle” is used to mean apivot cradle, a translation cradle, or a yoke.

In a tumble mode positioner, for example, the mounting unit is a pivotcradle; the test head pivots (or tumbles) about two oppositely disposedpivot points within the pivot cradle. This enables the user to tumblethe test head in the pivot cradle from a position where the devicehandler interface board is up (for interface to horizontal planehandlers from the bottom), through 180 degrees or more, to a positionwhere the device handler interface board is down (for interface tohorizontal plane handlers from the top). An example of a tumble modepositioner is disclosed in a previous patent by Smith (U.S. Pat. No.4,705,447), herein incorporated by reference.

In a cable pivot mode positioner, the test head pivots on the axis ofthe test head cables. Compared to the tumble mode positioner, a cablepivot mode positioner allows the use of reduced cable lengths. In manycable pivot positioners, the test head is rigidly attached to a yoke.The combination of yoke and test head are attached to the positioner ina manner that allows them to be rotated through 180 degrees or moreabout the axis of the test head cables for the previously mentionedpurposes. There are several ways of implementing cable pivot positionersas described for example in U.S. Pat. Nos. 5,900,737, 5,608,334,5,450,766, 5,241,870, 5,030,869, and 4,893,074.

Also, in both tumble mode and cable pivot positioners, it is typical toprovide a means to allow the test head to be pivoted at least a fewdegrees about an axis that is orthogonal to the axis that provides the180 degrees of rotation and that is parallel to the device handlerinterface. Thus the test head mounting unit may provide both pitch androll motions for the test head.

Still other positioners incorporate translation cradle mounting unitswhich provide translational in-out motion in addition to one or moreaxes of pivotal motion. The aforementioned U.S. Pat. Nos. 5,241,870 and5,450,766 provide examples of such units. In these examples the testhead is attached to slide units which slide in and out along twoparallel structures, which are arranged next to the two opposite sidesof the test head. Typically, the test head is attached to the slideunits so that it may pivot about the axis defined by the two points ofattachment.

Still further positioners do not use cradles. In one example, the testhead mounting unit comprises a gimbal-like mechanism internal to thetest head which provides rotational degrees of freedom to the test head.A first cable pivot axis supports the gimbal unit. The gimbal unitsupports a second axis, which is orthogonal to the first cable pivotaxis and parallel to the test interface board, and that directlysupports the test head. The test head may pivot about the second axis.

After a test head is docked with a device handler, the test head may bemaintained in an unlocked state relative to the axes about which itpivots. This may be done to allow the transmission of vibration from thedevice handler into the positioner system so that all of the vibrationis not absorbed by the fragile electrical connectors, which could bedestructive. In other words, by unlocking the axes of rotation so thatthe test head is in a “floating” state, vibrational forces aredissipated to the positioner system.

When a test head is situated in a positioner, it is desirable that thetest head pivot within the mounting unit about the center of gravity ofthe test head. “Center of gravity of the test head” with respect to apivot axis provided by the mounting unit means the center of gravity ofthe test head combined with the portions of the mounting units whichpivot with it and cables or other equipment effecting balance of thetest head within its mounting unit. While, during normal installation,the test head is attached to the mounting unit at the center of gravityof the test head, the center of gravity of the test head may change.This may occur, for example, if circuit boards are added (or removedfrom) the test head. Also, the center of gravity of the test head may beaffected by the cables that extend into the test head. It is common forthe cables to provide up to 30% of the total weight of the combinationof the cables and the test head.

Components of the mounting unit may pivot with the test head in one ormore axes. For example in a tumble mode system such as described in U.S.Pat. No. 4,705,447, the test head pivots with respect to the pivotcradle in a first axis, and the combination of the test head and pivotcradle pivot about an orthogonal axis. As another example in the cablepivot positioner shown in FIG. 7 of U.S. Pat. No. 5,450,766 the testhead and yoke pivot as a combined unit about a first axis, and the testhead yoke and other apparatus pivot as a unit about a second orthogonalaxis. It is highly desirable for each pivot axis to pass through itsrespective center of gravity. In these examples, the portion of themounting unit that pivots with the test head effectively becomes “part”of the test head to the extent it pivots with the test head.

If, however, the test head has not been positioned to pivot about acenter of gravity, and is hence unbalanced then gravitational forceswill try to urge the test head towards a balanced state. This may createa significant amount of stress on the test head pins through whichsignals are received from and transmitted to the device handler. As atest head may weigh 1000 kilograms (or more), if the center of gravityis offset by ⅛ inch (for example), the lateral forces which may beapplied to the test head pins as a result of this imbalance may beconsiderable. By applying such forces to the extremely small and fragilepins, the pins may become worn or damaged. Alternatively, as the testhead weight and imbalance may be supported by other structures (i.e.,cams and guide pins), these other structures may also become worn ordamaged by the imbalance. Thus, it is highly undesirable for the axisabout which the test head pivots to be offset from its center ofgravity.

In the past, the position of the test head in the mounting unit has beenadjusted by such techniques as swapping in supports of different lengths(until the test head is pivoting about its center of gravity) or using amultiple pivot point pivot cradle and changing the pivot point which isused to couple with the test head. Yet another technique to adjust thelocation of the center of gravity is to add or remove weights or ballastto or from the test head. All such techniques are cumbersome and mayrequire dismantling the equipment to provide the adjustment.

SUMMARY OF THE INVENTION

An apparatus is used for coupling a test head to a mounting unit inwhich the test head pivots. A base is attachable to a test head. Anextension member extends away from the test head. A slider slides awayfrom and towards a center of gravity of the test head. The slider isattachable to the mounting unit. An adjustment member extends from theextension member for fixing the position of the slider relative to thebase.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an apparatus for attaching a test headto a cradle in accordance with a first exemplary embodiment of thepresent invention.

FIG. 2 is another perspective view of the above apparatus in accordancewith a first exemplary embodiment of the present invention andaccommodating a certain center of gravity of the test head.

FIG. 3 shows the attachment unit of FIG. 2 in a position to accommodatea different center of gravity of the test head than what is accommodatedin FIG. 2.

FIG. 4 is an exploded perspective view of the apparatus shown in FIGS.1-3.

FIG. 5A is a perspective view which is useful for showing how the firstembodiment is used with a test head and a pivot cradle (which is atleast part of a mounting unit).

FIG. 5B is a perspective view which is useful for showing another way touse the first embodiment with a test head and a pivot cradle.

FIG. 6 is a perspective view of a second exemplary embodiment of thepresent invention.

FIG. 7 is an exploded view of the apparatus shown in FIG. 6.

FIG. 8A is a perspective view which is useful for showing how the secondembodiment is used with a test head and a pivot cradle.

FIG. 8B is a perspective view which is useful for showing another way touse the second embodiment with a test head and a pivot cradle.

DETAILED DESCRIPTION OF THE INVENTION

It is desirable to be able to change the location of a test head withinits mounting unit so that the test head pivots about its center ofgravity. To change the location of the test head within the mountingunit, attachment unit 100 is used. FIGS. 1, 2 and 3 are perspectivedrawings of attachment unit 100. Attachment unit 100 is comprised ofbody 110, slider 120 and adjustment member 142. Each separate piece willbe described in turn.

Body 110 includes a plurality of openings 140 a, 140 b, 140 c which areuseful for attaching attachment unit 100 to the test head. Thus, forexample, bolts may be placed through openings 140 a, 140 b, 140 c andsecured to the test head in order to attach body 110 to the test head.As is shown, raised portions 141 a,b,c may exist around openings 140 a,140 b, 140 c on the side of body 110 facing the test head. Raisedportions 141 a,b,c may add to the structural integrity of body 110 aswell as allowing more secure attachment of body 110 to the test head.

As shown in FIGS. 1-3, body 110 includes extension member 112. Extensionmember 112 extends from body 110. The purpose of extension member 112 isto accommodate adjustment member 142. Thus, extension member 112desirably includes an opening through which adjustment member 142 isinserted. In the embodiment shown in FIG. 1, extension member 112extends away from the test head. In an alternative embodiment, however,extension member 112 may extend from body 110 and towards the test head.

Body 110 also includes channel 114. Channel 114 is a portion of body110, and it accommodates slider 120. Thus, slider 120 is inserted intochannel 114. Slider 120 slides within channel 114 towards and away fromextension member 112.

Turning now to slider 120, slider 120 includes a plurality of openings130 a, 130 b. These openings may be used, for example, to accommodaterespective bolts which extend towards or away from the mounting unit inorder to attach slider 120 to the mounting unit. For example, if themounting unit comprises a pivot cradle, one opening (for example, 130 a)may be used as the pivot point of slider 120 relative to the pivotcradle (which is at least part of a mounting unit). The other opening(for example, 130 b) may be used to control the pivoting of slider 120relative to the pivot cradle. Thus, for example, by loosening a boltextending through opening 130 b, slider 120 is then permitted to pivotrelative to the pivot cradle to which it is attached. As a secondexample, if the mounting unit comprises a yoke, the openings 130 a and130 b may be used to rigidly attach slider 120 to the yoke using bolts.As shown, additional material may be placed around openings 130 a, 130 bin order to improve the structural integrity of slider 120 as well as toincrease the strength of the attachment between slider 120 and thecradle to which it is attached. One of ordinary skill in the art willrecognize that additional openings may be provided in slider 120 shouldthe application demand it. Also one skilled in the art will recognizethat the openings may be adapted to enabling appropriate fastening tovirtually any style of mounting unit.

As shown in the Figures, adjustment member 142 extends through extensionmember 112 and is secured to slider 120. Adjustment member 142 may have,for example, a threaded shaft which engages a threaded opening in slider120. Thus, by rotating adjustment member 142, slider 120 moves towardsand away from extension member 112. Looking, for example, in FIG. 2, byrotating adjustment member 142 in one direction, slider 120 movestowards extension member 112. Conversely, by rotating adjustment member142 in another direction, slider 120 moves away from extension member112.

FIG. 4 is an exploded view of attachment unit 100 which is useful forexplaining how the different parts which comprise attachment unit 100fit together. As is more clearly shown in FIG. 4, slider 120 may be heldwithin channel 114 as a result of the formation of a dovetail structure.Thus, angling the side walls 119 a, 119 b of channel 114 and angling theedges 124 a,b of slider 120 in order to coincide with the angle of sidewalls 119 a, 119 b creates a dovetail which helps to maintain slider 120within channel 114. This dovetail also allows slider 120 to easily slidewithin channel 114 as illustrated by FIGS. 2 and 3.

FIG. 4 includes plate 160. Plate 160 is attached to body 110 usingscrews 162 a, 162 b which are inserted through openings 161 a, 161 b.Screws 162 a, 162 b may then engage threaded openings 171 a, 171 b shownin FIGS. 2 and 3. The purpose of plate 160 is to ensure that slider 120is not permitted to slide sufficiently away from extension member 112 sothat it “falls out” of channel 114. Such a “falling out” would cause thetest head to detach from the cradle. This is an extremely undesirableoccurrence.

Also as shown in FIG. 4, slider 120 includes top section 127. Topsection 127 includes a plurality of openings 128 a, 128 b. Body 110 alsoincludes openings 117 a, 117 b, 117 c. Openings 117 a, 117 b, 117 c areshown in FIG. 4 in a triangle configuration. The triangle configurationensures that there is a sufficient amount of material between theopenings so that a crack does not form. It is contemplated, however,that openings 117 a, 117 b, 117 c may also be configured in a linearorientation.

Screw member 122 may be inserted into either opening 128 a or opening128 b. Openings 117 a, 117 b, 117 c are desirably threaded openingswhich may be engaged by screw member 122. Thus, as slider 120 slideswithin channel 114, one of openings 117 a, 117 b, 117 c will becomevisible either through opening 128 a or opening 128 b. By placing screwmember 122 through the appropriate opening (i.e., either opening 128 aor opening 128 b) and engaging the visible opening (i.e., opening 117 a,117 b, 117 c) from body 110, the position of slider 120 is more securelyfixed relative to body 110.

FIG. 5A illustrates how attachment unit 100 may be used to attach a testhead to a pivot cradle (which is at least part of a mounting unit). Asshown in FIG. 5A, test head 200 is shown with attachment locations 202a, 202 b, 202 c. Attachment locations 202 a, 202 b, 202 c may be, forexample, threaded openings. Pivot cradle 300 is also shown. Pivot cradle300 includes attachment location 302 at which the cradle is attached toattachment unit 100. Pivot cradle location 304 (which may be, forexample, a curved slot) is also provided in order to fix the pivotposition of test head 200 relative to pivot cradle 300. Thus, forexample, an appropriate threaded member may extend through attachmentlocation 302 in order to engage opening 130 a so that test head 200pivots about attachment location 302. Another attachment member (i.e.,bolt) may extend through pivot cradle location 304 in order to engageopening 130 b. As the test head 200 pivots about attachment location302, the bolt may move in an arc along pivot cradle location 304. Bytightening the bolt within pivot cradle location 304, pivoting of testhead 200 relative to pivot cradle 300 is stopped.

It will be appreciated that in FIG. 5A attachment unit 100 is part ofthe mechanism that allows test head 200 to pivot in pivot cradle 300.One of ordinary skill in the art will recognize that attachment unit 100may be readily attached by way of openings 130 a, 130 b to a widevariety of alternative structures or mechanisms which are considered tobe mounting units. Thus, it may be rigidly attached to a yoke. As afurther example it may be rigidly attached to a bearing mechanism thatis also attached to the mounting unit to facilitate low frictionpivoting. This would facilitate using attachment unit 100 to attach atest head 200 to a translation cradle or a gimbal mechanism.

In practice, additional circuit boards may be added to test head 200.Alternatively, circuit boards may be taken away from test head 200.These additions or deletions will change the center of gravity of testhead 200. The present invention allows the position of test head 200within a mounting unit such as pivot cradle 300 to be changed in orderto accommodate a changed center of gravity. Thus, if the center ofgravity of test head 200 changes, then screw member 122 may be removedfrom hole 128 a or 128 b and adjustment member 142 may be rotated inorder to change the position of body 110 relative to slider 120. In theillustrated exemplary embodiment, adjustment member 142 is a threadedmember which engages threaded opening 126 in slider 120. By rotatingadjustment member 142, slider 120 slides towards or away from extensionmember 112. By inserting and tightening screw member 122 in theappropriate hole, the location of slider 120 relative to body 110 isfurther fixed. If the center of gravity of test head 200 is movedtowards the front of test head 200 (i.e., toward face 200 a), test head200 may be moved back by rotating adjustment member 142 so that slider120 is in the position shown in FIG. 2. Alternatively, if the center ofgravity of test head 200 is moved towards the back of the test head(i.e., away from front face 200 a), adjustment member 142 may be rotatedso that slider 120 is closer to (but not necessarily in) the positionshown in FIG. 3. Screw member 122 is loosened and tightened as needed sothat slider 120 may slide and then be fixed in position.

It will be understood to one of ordinary skill in the art that it ispreferred to use two attachment units 100, one on each side of test head200.

In FIG. 5A, pivot cradle 300 is attached to slider 120 and test head 200is attached to base 110. It is understood, however, that there are otherways by which attachment unit 100 may be used to couple together amounting unit such as pivot cradle 300 and test head 200. For example,as shown in FIG. 5B, attachment unit 100 may be used in an orientationwhich is the reverse of the orientation shown in FIG. 5A. Thus, in theorientation shown in FIG. 5B, extension member 112 extends towards thetest head 200. As shown in FIG. 5B, slider 120 may be attached to testhead 200 via openings 130 a, 130 x, 130 b and attachment locations 202c, 202 b, 202 a, respectively. Furthermore, body 110 may be attached topivot cradle 300 via openings 140 a, 140 b and pivot cradle location304, attachment location 302, respectively. Thus, slider 120 moves withtest head 200 in order to change the location of the center of gravityof test head 200 relative to the axis about which test head 200 rotates.One of ordinary skill in the art will recognize that attachment unit 100may be readily attached by way of openings 140 a, 140 b, 140 c to a widevariety of alternative structures or mechanisms. Thus, it may be rigidlyattached to a yoke. As a further example it may be rigidly attached to abearing mechanism that is also attached to the mounting unit tofacilitate low friction pivoting. This would facilitate using attachmentunit 100 to attach a test head 200 to a translation cradle or a gimbalmechanism. It is also readily understood that the attachment unit 100 isuseful in adjusting the position of the center of gravity of the testhead in combination with any apparatus that pivots together with itabout the axis of interest. Thus, for example, attachment unit 100 isuseful in adjusting the center of gravity combined with the yoke withrespect to the pitch axis in a cable pivot system.

A further exemplary embodiment of the present invention is shown inFIGS. 6-8B. The embodiment shown in FIGS. 6-8B differs from theembodiment shown in FIGS. 1-5B in that, in the embodiment shown in FIGS.1-5, adjustment may be made with one degree of motion. In the embodimentshown in FIGS. 6 and 7, adjustment may be made in two degrees offreedom. Thus, the second embodiment allows the position of the testhead within the cradle to be modified in a first direction and in asecond direction orthogonal to the first direction through the use ofattachment unit 201.

As shown in FIGS. 6 and 7, the second embodiment shares somesimilarities with the first embodiment. Thus, for example, body 110 isincluded. Extension member 112 extends from body 110. Adjustment member142 is accommodated by extension member 112. Adjustment member 142extends through extension member 112 and is secured to slider 120. FIG.8A illustrates attachment unit 201 used with a mounting unit thatcomprises a pivot cradle. Here an appropriate threaded member may extendthrough the pivot cradle in order to engage opening 130 a so that testhead 200 pivots about opening 302. Another attachment member may extendthrough attachment location 304 in order to engage opening 130 b. As wasthe case with the previously described attachment unit 100, attachmentunit 201 may be readily attached to any type of mounting unit.

The second exemplary embodiment differs from the first exemplaryembodiment in that, in the second exemplary embodiment, a tongue portion224 extending from the bottom of body 110 includes side walls 224 a and224 b which are sloped to form a dovetail profile. The function of sidewalls 224 a and 224 b will be explained below.

As shown in FIGS. 6 and 7, secondary body 210 is included. Secondarybody 210 includes secondary extension member 212. Secondary extensionmember 212 extends from secondary body 210. The purpose of secondaryextension member 212 is to accommodate secondary adjustment member 242.Thus, secondary extension member 212 desirably includes an openingthrough which secondary adjustment member is inserted.

Secondary body 210 also includes secondary channel 214 with sloped sidesto match the cross section of tongue portion 224. Secondary channel 214is a portion of secondary body 210 which accommodates body 110. Thus,tongue portion 224 is inserted into secondary channel 214. Tongueportion 224 of body 110 slides within secondary channel 214 towards andaway from secondary extension member 212.

As shown in FIGS. 6-8B, adjustment member 242 extends through secondaryextension member 212 and is secured to body 110 through, for example, athreaded opening (not shown) in body 110. Secondary adjustment member242 may have, for example, a threaded shaft which engages a threadedopening (not shown) in body 110. By rotating secondary adjustment member242, body 110 moves towards and away from secondary extension member212. Thus, by rotating secondary adjustment member 242 in one direction,body 110 moves towards secondary extension member 212. Conversely, byrotating secondary adjustment member 242 in another direction, body 110moves away from secondary extension member 212.

FIG. 7 is an exploded view of attachment unit 201 which is useful forexplaining how the different parts which comprise attachment unit 201fit together. As is more clearly shown in FIG. 7, body 110 may be heldwithin secondary channel 214 as a result of the formation of an optional“dovetail” structure. Thus, angling the side walls 219 a, 219 b ofchannel 214 and angling the edges 224 a, 224 b extending from the bottomof body 110 in order to coincide with the angle of side walls 219 a, 219b creates a dovetail which helps to maintain body 110 within channel214. This dovetail also allows body 110 to easily slide within channel214. Plate 260 is included. Plate 260 is attached to secondary body 210using screws 262 a, 262 b which are inserted through openings 261 a, 261b. Screws 262 a, 262 b may then engage threaded openings 217 a, 217 bshown in FIG. 7. The purpose of secondary plate 260 is to ensure thatbody 110 is not permitted to slide sufficiently away from extensionmember 212 so that it “falls out” of secondary channel 214. Again, sucha “falling out” would cause the test head to detach from the cradle.This is an extremely undesirable occurrence.

The above description has referred to a dovetail. It is understood thatother configurations (for example, a “T” slot) may be used.

Secondary body 210 includes openings 240 a, 240 b, 240 c which areuseful for attaching attachment unit 200 to the test head. Thus, forexample, as shown in FIG. 8A bolts may be placed through openings 240 a,240 b, 240 c and secured to the test head in order to attach secondarybody 210 to the test head. Raised portions (of which only portion 241 ais shown) may exist around openings 240 a, 240 b, 240 c on the side ofsecondary body 210 facing the test head. The raised portions may add tothe structural integrity of secondary body 210 as well as allowing moresecure attachment of secondary body 210 to the test head.

In practice, attachment unit 201 allows the position of the test headrelative to the mounting unit to be adjusted with two degrees offreedom. Thus, the position of the test head with respect to the pivotpoint in the mounting unit may be changed in order to accommodate achanged center of gravity. If the center of gravity of test head 200changes along one axis, adjustment member 142 may be rotated in order tochange the position of slider 120 relative to body 110 so that the testhead can pivot about its center of gravity. Furthermore, if the centerof gravity of test head 200 changes along a second axis orthogonal tothe first axis, secondary adjustment member 242 may be rotated in orderto change the position of secondary body 210 relative to body 110. Thus,for example, if the center of gravity of test head 200 is moved towardsthe front of test head 200 (i.e., toward face 200 a), test head 200 maybe moved back by rotating adjustment member 142. Alternatively, if thecenter of gravity of test head 200 is moved towards the back of the testhead (i.e., away from front face 200 a), adjustment member 142 may berotated in the opposite direction so that test head 200 may be movedforward. If the center of gravity of test head 200 is moved towards thetop of test head 200 (i.e., towards top 200 b), test head 200 may bemoved downward by rotating secondary adjustment member 242 so that testhead 200 may be moved down. Alternatively, if the center of gravity oftest head 200 is moved towards the bottom of the test head (i.e., awayfrom top face 200 b), secondary adjustment member 242 may be rotated sothat test head 200 may be moved up.

As previously discussed with regard to the embodiment shown in FIGS. 5Aand 5B, screw member 122 is loosened and tightened as needed so thatslider 120 may slide and then be fixed in position. Screw member 222 isloosened and tightened as needed so that body 110 may slide and then befixed in position. Screw member 222 may engage one of the openings 216a, 216 b, 216 c formed in secondary body 210 through an opening in body110. Thus, when screw member 222 engages one of the openings 216 a, 216b, 216 c in secondary body 210, body 110 is fixed in position relativeto secondary body 210.

Thus, as shown in FIG. 8A, slider 120 is coupled to pivot cradle 300 andsecondary body 210 is coupled to test head 200. It is understood,however, that there are other ways in which attachment unit 201 can beused to couple together test head 200 and pivot cradle 300. As shown,for example, in FIG. 8B, the orientation of attachment unit 201 may beeffectively rotated relative to the orientation shown in FIG. 8A. Thus,as shown in FIG. 8B, test head 200 is coupled to slider 120 viaattachment locations 202 a, 202 b, 202 c and openings 130 b, 130 x, 130a, respectively. Furthermore, secondary body 210 may be coupled to pivotcradle 300 via openings 240 a, 240 c and pivot cradle location 304,attachment location 302, respectively. Thus, as body 110 or slider 120moves, test head 200 moves along with body 110 and/or slider 120. It isunderstood, however, that attachment unit 201 may be readily used toattach a test head to numerous types and styles of mounting units in oneof two basic ways. In the first, secondary body 210 is attached to thetest head and slider 120 is attached to the mounting unit. In thesecond, slider 120 is attached to the test head and secondary body 210is attached to the mounting unit. If the mounting unit comprises a yoke,the attachment to the yoke is done rigidly. If the mounting unitcomprises a translation cradle or gimbal mechanism, the attachment maybe effected with bearing units to facilitate pivoting of the test head.Attachment to a pivot cradle may also be effected with bearing units ifit is so desired.

It is furthermore readily understood that the attachment unit 210 isuseful in adjusting the position of the center of gravity of the testhead in combination with any apparatus that pivots together with itabout the axis of interest. Thus, for example, attachment unit 100 isuseful in adjusting the center of gravity combined with the yoke withrespect to the pitch axis in a cable pivot system.

In FIG. 8B, body 110 is shown in the drawing as sliding vertically whileslider 120 is shown as moving horizontally. It is understood, however,to one of ordinary skill in the art that body 110 and slider 120 may beredesigned so that body 110 moves horizontally relative to secondarybody 210 (as shown) and slider 120 moves vertically relative to body 110(as shown).

While preferred embodiments of the invention have been shown anddescribed herein, it will be understood that such embodiments areprovided by way of example only. Numerous variations, changes andsubstitutions will occur to those skilled in the art without departingfrom the spirit of the invention. Accordingly, it is intended that theappended claims cover all such variations as fall within the spirit andscope of the invention.

1. An apparatus for coupling a test head to a mounting unit in whichsaid test head pivots, said apparatus comprising: a base having aplurality of base attachment locations at which said base attaches toone of said test head and said mounting unit; a slider which slides awayfrom and towards a center of gravity of said test head, said sliderincluding at least one slider attachment location at which said sliderattaches to another of said test head and said mounting unit; and anadjustment member for changing a position of said slider relative tosaid base.
 2. An apparatus for coupling a test head to a mounting unitaccording to claim 1, wherein said base includes an extension memberextending away from said test head and wherein said adjustment memberextends from said extension member for fixing the position of the sliderrelative to the base.
 3. An apparatus for coupling a test head to amounting unit according to claim 1, wherein said base includes anextension member extending towards said test head and wherein saidadjustment member extends from said extension member for fixing theposition of the slider relative to the base.
 4. An apparatus forcoupling a test head to a mounting unit according to claim 1, whereinsaid sliding member slides within a channel formed in said base.
 5. Anapparatus for coupling a test head to a mounting unit according to claim1, further comprising a secondary base which slides away from andtowards said center of gravity of said test head in a direction havingan orthogonal component relative to a further direction in which saidslider slides.
 6. An apparatus for coupling a test head to a mountingunit according to claim 5, wherein said secondary base is situatedbetween said slider and said base.
 7. An apparatus for coupling a testhead to a mounting unit according to claim 5, further comprising afurther adjustment member for changing a further position of saidsecondary base relative to said base.
 8. An apparatus for coupling atest head to a mounting unit in which said test head pivots, saidapparatus comprising a base having a slider which slides relative tosaid base; a first location of said base for attaching said base to oneof said test head and said mounting unit; a second location of saidslider for attaching said slider to another of said test head and saidmounting unit; and a fastening device for preventing sliding of saidslider relative to said base.
 9. An apparatus for coupling a test headto a mounting unit according to claim 8, wherein said base includes anextension member extending away from said test head and wherein saidadjustment member extends from said extension member for fixing theposition of the slider relative to the base.
 10. An apparatus forcoupling a test head to a mounting unit according to claim 8, whereinsaid base includes an extension member extending towards said test headand wherein said adjustment member extends from said extension memberfor fixing the position of the slider relative to the base.
 11. Anapparatus for coupling a test head to a mounting unit according to claim8, wherein said sliding member slides within a channel formed in saidbase.
 12. An apparatus for coupling a test head to a mounting unit inwhich said test head pivots, said apparatus comprising: base means forbeing attached to one of said test head and said mounting unit; slidermeans for sliding away from and towards a center of gravity of said testhead; and adjustment means for changing a position of said base meansrelative to said slider means.